(a) Technical Field
The present invention relates to an offset compensation method and system of a hall sensor in a motor, and more particularly, to an offset compensation method of a hall sensor in a motor that can prevent a detection error regarding the position of the motor rotor.
(b) Background Art
Eco-friendly vehicles including fuel cell vehicles, electric vehicles, hybrid vehicles, and plug-in electric vehicles are equipped with a plurality of motors for electricity generation and driving, and are equipped with hall sensors for detecting the revolutions per minute (RPM) of each motor to more accurately control the driving of the motors. The hall sensors are disposed at a particular angle on certain positions of each motor, and generate on or off digital signals when the rotor of the motor rotates to output the position information of the rotor. Based on the position information of the rotor, a series of motor driving controls (e.g., calculation of motor speed) may be executed.
Further, a blower configured to supply air into a fuel cell system, i.e. an air blower having a form in which an aerodynamic part is added to a motor includes a Surface Mounted Permanent Magnetic Synchronous Motor (SMPMSM), and a hall sensor that is a type of position sensor to detect the position of the rotor and measure the speed of the rotor. The hall sensor is mounted onto the end plate side of a cylindrical motor housing, and three hall sensors are disposed at a uniform interval of 120 degrees to measure the rotation speed of tens of thousands of RPM.
A controller (e.g., three-phase voltage-type inverter, hereinafter, referred to as “inverter”) connected to the air blower is configured to configured direct current (DC) power of high-voltage terminal into three-phase alternating power using Space Vector Pulse Width Modulation (SVPWM) to rotate an electric motor. Thus, a coaxial impeller is configured to supply air into the fuel cell system by pushing air while rotating. To rotate the rotor using an attractive force and a repulsive force between the rotor (e.g., permanent magnet) and the rotating magnetic field generated using SVPWM control of the permanent magnet motor, the position of the rotor magnet should be accurately measured. However, since the position of the rotor magnet is measured by the output value based on the arrangement of the hall sensor mounted onto the motor housing, the manufacturing error that occurs upon mounting of the hall sensors may cause the speed error and the position error of the rotor.
Hereinafter, a typical operation of detecting the position of the motor rotor using hall sensors will be described below.
FIG. 1 is an exemplary view illustrating an arrangement structure of a stator, a rotor, and hall sensors of a motor. When an air blower is manufactured to supply air into a fuel cell system, three hall sensors A, B and C are mounted within the housing at a uniform interval of 120 degrees. The housing also includes a stator and a winding.
Accordingly, upon application of a U-phase current of three-phase coordinate system, an angle offset between the position (hereinafter, referred to as U-phase position) at which a magnetic field is generated and the hall sensor A is a ‘rotor position offset’, and this rotor position offset is stored within a controller to be used to measure the position of the rotor. Thus, when the position of the rotor is measured, it may be assumed that the hall sensors A, B and C are accurately disposed at an angle of 120 degrees and that the hall sensor A and the U-phase position have an accurate angle offset.
FIG. 2 is an exemplary view illustrating a measurement process of a hall sensor when the rotation direction of the rotor is determined based on the movement of a rotating magnetic field. In particular, the rotation direction of the rotor is determined based on the movement of the rotating magnetic field of the motor. The position of the rotor is measured using output values of the hall sensor.
The hall sensor is configured to output high in N-polar direction, and output low in S-polar direction. Additionally, since the hall sensors A, B and C are disposed at an interval of 120 degrees, the output changes of the hall sensors may occur six times per one rotation of the rotor. The output values of the hall sensors are described in Table 1 below.
TABLE 1
As described in Table, a section that the N-polar of the rotor faces is determined based on the output value of the hall sensors. Additionally, the direction is determined based on the changing order of each hall sensor. However, when the installation positions of the hall sensors deviate from desired positions, the position of the rotor by the rotating magnetic field and the section based on the position of the hall sensors shown in FIG. 2 may be sensed as different from the actual position of the rotor.
In other words, the position error that occurs during the mounting of the hall sensor A having an offset falling within an allowable error in the U-phase position of the stator winding, i.e., the position error that occurs in a process of mounting the hall sensors B and C at intervals of 120 degrees and 240 degrees with respect to the hall sensor A affects the change of the output value of the hall sensors, causing the calculation error of the speed and position of the rotor.
Furthermore, the speed error of the rotor may cause a ripple in regard to an output current command of a speed controller, reducing the stability of a current controller. In addition, the position error of the rotor may be an error of the rotor position angle used in the current controller, causing a ripple of a three-phase motor output current and thus reducing the electrical efficiency and causing heating of the motor as well as wobble of the motor rotation speed.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.